1. Field of the Invention
The present invention relates to an image forming apparatus that is capable of handling encoded images, a control method for the image forming apparatus, a program, and a storage medium.
2. Description of the Related Art
For guarantee of authenticity, prevention of tampering, and/or attachment of additional information for an important document, the following technique is known. Information is encoded to generate an encoded image, and the generated encoded image is formed and printed on a sheet (i.e., a printing medium) with an image of a document.
Then, the printed image on the sheet is read with a reader, the encoded image is extracted from information that has been read off, and the extracted encoded image is decoded to retrieve information.
The contents of a printed encoded image cannot be recognized by a user as it is. By capturing the encoded image as image data using a reader and applying corresponding decoding processing to the image data, the user can recognize the contents of the encoded image.
In general, image data that has been read off is transferred to a computer and decoded by an application program that runs on the computer. Aside from this method, however, an encoded image can also be decoded inside a reader by means of a mobile telephone that supports two-dimensional codes, or can be decoded inside a copying machine having a number of functions.
An encoded image is typically made up of dots, and is formed and printed on a sheet together with text and/or images which are to be printed with a size that allows the dots to be reliably recognized as dots of an encoded image when being read by a reader.
As a technique for printing an encoded image on a sheet, a technique is generally known that embeds code information which gives directivity to a calculated rectangular size in consideration of an encoded image and the size of paper sheets for printing (e.g., Japanese Patent Application Laid-Open No. 2003-101762).
However, conventional generation processing of an encoded image does not take into consideration the printing characteristic of an output device (e.g., a copier and a printer) that varies with differences between individual machines, environmental changes, and lapse of time. Accordingly, even if an encoded image is generated with dot data of a predetermined size that can be recognized as dots, the dots become smaller due to variation of the printing characteristic of the output device and cannot be recognized as dots at the time of reading. This problem leads to a problem that the encoded image cannot be recognized as an encoded image at the time of reading.
The present invention has been made in view of these problems and has an object of preventing an encoded image that will be unrecognizable as an encoded image at the time of reading from being printed on a sheet.